Which technique is best for preserving plastic fingerprint impressions?

The technique of using silicone rubber casting is the most effective method for preserving plastic fingerprint impressions. Plastic prints are unique because they are three-dimensional impressions left in a pliable surface, such as soft materials like wax, clay, or some types of paint.

Silicone rubber casting allows for the creation of a highly detailed negative impression of the fingerprint, capturing all the nuances of the ridge patterns that are critical for identification. Once the silicone rubber has set, it can be removed carefully to retain the exact shape and structure of the print. This method provides a durable preservation of the impression that can be analyzed and compared later, which is essential for forensic investigations.

In contrast, other methods such as powder dusting or superglue fuming are more suitable for two-dimensional latent prints found on non-porous surfaces. Dusting with powder cannot capture the full depth of a plastic print, while superglue fuming works primarily by bonding to moisture left by sweat on the surface of the ridges of a print, which does not apply to the three-dimensional nature of plastic prints. Ink and paper methods are typically used for recording known fingerprints rather than preserving those that are left at a crime scene.